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Moon and Regulus

Regulus is a big star — it’s three times the Sun’s diameter. Even so, the heart of the lion will wink out of sight in an instant early tomorrow for skywatchers across almost all of the United States.

Nothing is happening to the star itself. Instead, it’ll be covered by the crescent Moon — an event known as an occultation. It’s one of a series of occultations that began last December and will continue through April.

The Moon can occult Regulus because the star lies right on the ecliptic, which is the Sun’s path across the sky. The Moon stays close to that path, too. But the Moon’s orbit is tilted a bit with respect to the ecliptic. So most months, the Moon misses Regulus.

In fact, it misses the star most years as well. That’s because the Moon veers back and forth across the ecliptic over a period of years. So its occultations of Regulus come in clumps — when the Moon’s position relative to the ecliptic is just right.

This occultation begins in the wee hours of the morning — around 5:45 a.m. from New York, and earlier as you move farther west. Regulus will disappear behind the lighted portion of the Moon, then return to view from the dark portion. The occultation will last about 30 minutes to an hour, with Regulus remaining hidden longer from more southerly latitudes.

Those on the Pacific coast won’t see the occultation at all — it’ll be over by the time the Moon and Regulus rise, with the bright star standing just above the Moon.

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